The present invention relates to a process and apparatus for combusting refuse, and especially to a process for burning of waste material including polyvinyl chloride or similar plastics which may produce phosgene upon combusting at certain temperatures without so producing such phosgenes.
Public landfills are rapidly overflowing with residential and commercial waste products. Trash disposal has become a serious problem, and many cities, municipalities, corporations or other entities which may have a need to dispose of trash, are looking to alternative means of disposing of such trash. One potential source of such disposal is by combustion of a large percentage of the trash. Such combustion produces substantial quantities of heat which may be beneficially used and may produce other byproducts such as fertilizer. Certain other portions of the trash may be also recovered for beneficial use, for example, metal components. In typical residential and commercial waste, as much as 5000 Btu of heat energy is recoverable from each pound of such waste. The volume of the waste may also be reduced as much as 90% to 95% in a combusting process.
A major problem related to the burning of commerical and industrial waste is the unwanted production of phosgene gas. Phosgene normally results from the burning of certain plastics, in particular, polyvinyl chloride (PVC) at temperatures above 1200 degrees F. (Fahrenheit) or greater in the presence of excess oxygen. Such PVC is present in essentially all trash which is normally dumped in landfills in the form of plastic bottles, plastic trashbags or the like. Phosgene is a pollutant gas which may be hazardous to health of people or animals living near the discharge of such gas. Therefore, the emission of this gas is regulated by pollution control laws. Conventional trash burning processes typically produce substantial amounts of phosgene and require special reforming equipment through which the gasses exiting such conventional processes must be passed so as to convert the phosgene to a nonhazardous substance. Such reforming processes are typically quite expensive to operate which has substantially dampened the demand for trash burning processes.
It has been found that in order to control the amount of phosgene produced by a process burning PVC, it is necessary to carefully control the temperature and the amount of oxygen allowed to enter the process burning the trash until such trash has been fully carbonized. After carbonization of the trash, wherein a gas having a high Btu content is formed, such gas when subsequently burned, is less likely to form phosgene and may be removed from the process and burnt in the presence of excess oxygen. In order to control the temperature and the amount of oxygen present during the carbonization step, it is necessary to carefully control the amount of oxygen entering into the burning chamber. While a rotary kiln or furnace has been utilized in the past and is highly effective in burning trash, it is difficult to fully regulate the amount of oxygen entering into the burning chamber, especially as there are typically wide gaps between the ends of the rotary portion of the furnace and stationary heads associated with those ends. Because of the high temperatures associated with the furnaces and the continual wear thereon, previous seals at the juncture of the rotary portion of the furnace and the stationary heads have typically been ineffective. It is further noted that suitable seals must be provided whereat trash enters the process and whereat noncombusted trash and gasses exit the process.
It has further been found that furnaces including refracted tiles typically are difficult to control temperature wise and also that in some instances additional cooling must be added as a jacket or the like to maintain temperatures within the furnace below phosgene producing temperatures.